2000 年 34 巻 3 号 p. 169-189
This paper reviews three topics on the spectroscopic approach to the natural carbonaceous materials, especially focuses on photoluminescence (PL) spectroscopy of natural polycrystalline diamonds and Raman spectra deciphering chemical structure of graphite. The first topic is characteristic PL spectra of carbonado natural polycrystalline diamond whose origin has been in enigma. We have shown that carbonado from Central African Republic can be grouped into two groups according to the structure of PL spectra. PL of carbonado resulted from radiation-induced damage and interaction with thermal fluids. Carbon isotope composition, thermal behavior, REE abundance correlate with PL. We suggested that the characteristics of carbonado were induced at the last stage by reaction with thermal fluids. The second is micro Raman spectroscopy characterizing the chemical structure of graphitic material in ureilite. We proposed array plots between Raman frequency of E2g mode of graphite and intensity ratio of G-band to D-band. The distribution in the array plots was proved to be closely linked to the extent of shock which ureilites suffered. The third is on the technical caution on micro-Raman spectroscopy. Laser-induced heating during measurements of micro-Raman spectra, in some cases, gives rise to considering downshifts in Raman spectra of powder samples. We showed that the intensity ratio of Stokes line to Anti-Stokes line is potential to monitor the temperature of sample surface to cancel out the artificial downshifts. Furthermore, we demonstrated that the stacking sequences of graphite did not affect the intralayer vibrational frequency.
